300b lovers

I have been an owner of Don Sachs gear since he began, and he modified all my HK Citation gear before he came out with his own creations.  I bought a Willsenton 300b integrated amp and was smitten with the sound of it, inexpensive as it is.  Don told me that he was designing a 300b amp with the legendary Lynn Olson and lo and behold, I got one of his early pair of pre-production mono-blocks recently, driving Spatial Audio M5 Triode Masters.  

Now with a week on the amp, I am eager to say that these 300b amps are simply sensational, creating a sound that brings the musicians right into my listening room with a palpable presence.  They create the most open vidid presentation to the music -- they are neither warm nor cool, just uncannily true to the source of the music.  They replace his excellent Kootai KT88 which I was dubious about being bettered by anything, but these amps are just outstanding.  Don is nearing production of a successor to his highly regard DS2 preamp, which also will have a  unique circuitry to mate with his 300b monos via XLR connections.  Don explained the sonic benefits of this design and it went over my head, but clearly these designs are well though out.. my ears confirm it. 

I have been an audiophile for nearly 50 years having had a boatload of electronics during that time, but I personally have never heard such a realistic presentation to my music as I am hearing with these 300b monos in my system.  300b tubes lend themselves to realistic music reproduction as my Willsenton 300b integrated amps informed me, but Don's 300b amps are in a entirely different realm.  Of course, 300b amps favor efficient speakers so carefully component matching is paramount.

Don is working out a business arrangement to have his electronics built by an American audio firm so they will soon be more widely available to the public.  Don will be attending the Seattle Audio Show in June in the Spatial Audio room where the speakers will be driven by his 300b monos and his preamp, with digital conversion with the outstanding Lampizator Pacific tube DAC.  I will be there to hear what I expect to be an outstanding sonic presentation.  

To allay any questions about the cost of Don's 300b mono, I do not have an answer. 




Hi @donsachs ​​​​@lynn_olson ,


I have 300B SET with 6f6 driver in triode mode. I did 2nd harmonic distortion calculation using 3 point method and 6f6 plate characteristic graph. So with RC coupling that I have right now I get more than 2% distortions with voltage swing 140v pick to pick and when I go to interstage transformer coupling I can get around 0.7% distortions with 160v pick to pick. The difference is huge!

I have a couple of question about using transformer. Do you use load a resistor after the interstage transformer? What kind resistors do you use? I'm going to use Hashimoto A-305 transformers. As I understand Hashimoto recommends 100K load resistor for this transformer.





I am sorry, but I am not giving anything about the design of the amp away.  I had ITs custom wound for the project.   My amp is PP, but if you need a load resistor with your circuit then I would try two kinds.  A good quality wirewound of sufficient rating, and a good old Kiwame 2W or 5W depending on what you need.   I usually use wirewounds, and not cheap ones, but Ohmite or Vishay or something else of quality.  Which you prefer will depend on the circuit, your ear, and the Hashimoto iron.  The resistors are cheap so try both kinds and see what you think.

There is a simple and inexpensive means of dealing with heat due to amplification. Ducts in the ceiling above the amplifier(s) can be added, along with dryer style hose the connects via a squirrel fan to the outside. This can be installed for a few hundred dollars (mostly labor), is quieter and far less power draw than air conditioning. 

Do you use load a resistor after the interstage transformer? What kind resistors do you use?

@alexberger If any audio transformer is not loaded it can 'ring' (which is to say it will generate harmonic distortion, which can be quite profound). The correct loading will cause a state of 'critical damping' in the transformer, where when a square wave is put thru the device, it will have little or no 'overshoot'. Since the grid of a tube tends to be very high impedance (other than its capacitance) some form of resistive loading is a good idea to explore!

Since you sound like you are up to something with your own design, I recommend an empirical approach, which might be to drive the transformer with a square wave and have it drive in turn a power tube which is operating normally. A potentiometer and oscilloscope's probe across the output of the transformer would then allow you to vary the potentiometer and observe the result on the square wave. In this manner you can exactly dial in the correct loading value.

I agree with Atmasphere. Some things cannot be accurately modeled. Put it on a bench, attach a dummy load, light it up, and measure square waves. Tune for nice-looking leading (and trailing) edges. Measure both low-level (below 1 watt) and also just below clipping.